There were at least two models: a compact headset (used aboard Jem'Hadar attack ships) and a larger shoulder-mounted version (used aboard Jem'Hadar battle cruisers). Dominion ships were normally equipped with only two display devices: one for the Vorta commander and the other for the Jem'Hadar First. (DS9: "The Ship") The virtual display device gave the wearer the ability to view the space around the ship by simply turning his or her head (or as Elim Garak said, "It's like having a viewscreen inside your brain"). (DS9: "Rocks and Shoals")